Technical Field
Embodiments of the inventive concept relate to a semiconductor device having a stressor.
Discussion of Related Art
In a field-effect transistor (FET), the drain-to-source current flows via a conducting channel that connects the source region to the drain region. The conductivity is varied by the electric field that is produced when a voltage is applied between the gate and source terminals. A metal-oxide-semiconductor FET (MOSFET) is a type of FET used for amplifying or switching electronic signals.
Performance of a transistor may be improved by increasing a carrier mobility inside a channel area of the channel of the transistor. A technique of forming stressors at both sides of the channel area has been tried to increase mobility. However, the stressors are vulnerable to cracking or other defects due to differences in a thermal expansion coefficient and a lattice constant. The thermal expansion coefficient describes the relative change in length of a material per degree of temperature change. The lattice constant refers to the physical dimension of unit cells in a crystal lattice. Cracks in a stressor of a transistor may cause a decrease in the tensile strength of the stressor, and cause a leakage current in the transistor.